Biophysics of Recombination Intermediates inNed Seeman's Laboratory

All of the programs in this laboratory have been derived from biophysical work on branched DNA molecules, called Holliday junctions, that function as ephemeral
intermediates in the process of genetic recombination.
This process results in the exchange of genetic information between two molecules of DNA. The branch point in naturally-occurring Holliday junctions is mobile, because it contains homologous (twofold) sequence symmetry. This feature makes Holliday junctions hard to study. We have devised means to eliminate sequence symmetry, thereby producing an
immobile branched junction.
We have characterized features of these molecules relating to their structure, their thermodynamics and their structural transformations. Sometimes a recombinational intermediate contains two crossovers. We have characterized these
double crossover molecules,
which come in five basic isomeric types. We have used these molecules to establish some of the features of symmetric Holliday junctions, such as crossover topology, susceptibility to resolvases, and base-stacking preferences. Recently, we have learned more about the features of the Holliday junction by making arrays from Holliday junction parallelograms, and from Bowtie junction parallelograms.